Process for improved flotation treatment of iron ores by selective flocculation



Dec. 20, 1966 PROCESS D. W. FROMMER ETAL FOR IMPROVED FLOTATION TREATMENT OF IRON ORES BY SELECTIVE FLOCCULATION Filed May 4, 1964 IRON ORE

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SODIUM SILIGATE OVERFLDW C O TAPIOOA FLOUR CALCIUM CHLORIDE OVERSIZE RETURN OVERFLOW WASTE "1 I THICKENER v (n NgDH SODIUM SILIOATE FLOCCULATED TAPIOOAFLOUR l UNDERFLOW I i I l I f l CONDITIONERS E THlCKENER l i FLOTAT'ON CELLS l FLOCCULATED l UNDERFLOW l l l I J INVENTORS ATTORNEY S United States Patent 3,292,780 PROCESS FOR HVIPROVED FLOTATION TREAT- MENT OF IRON ORES BY SELECTIVE FLOC- CULATION Donald W. Frommer and Arthur F. Colombo, both of Bloomington, Minn, assignors to the United States of America as represented by the Secretary of the Interior Filed May 4, 1964, Ser. No. 364,861 10 Claims. (Cl. 209-) The invention herein described and claimed may be used by or for the Government of the United States of America for governmental purposes without the payment of royalties thereon or therefor.

This invention relates to concentration of iron ores for use in iron and steel making.

Reverse (silica) flotation processes, especially anionic flotation of silica, have been employed for production of high grade iron ore concentrates. These processes are frequently more effective than flotation of the iron minerals. Such processes, however, frequently require grinding of the ore to very fine sizes, resulting in reduction of some of the silica to slime that shows reluctant response to flotation. Utilization of conventional desliming processes to overcome this difficulty usually results in excessive iron losses.

It is therefore an object of the present invention to provide a method for removel of slimed silica to enable effective utilization of flotation processes on the deslimed residue.

It has now been found that this objective may be accomplished by dispersion of the finely ground ore, preferential flocculation of iron oxides and removal of slimed silica prior to treatment of the deslimed residues by conventional flotation methods.

The invention will be more specifically described with reference to the flow diagram of the figure. Water and dispersants (NaOH and sodium silicate), along with ore, are introduced to a grinding mill. The specific dispersants used, their concentration, pH, etc., are not critical and will vary with the particular ore, state of subdivision of the ore, etc. The function of these materials is simply to provide a uniform dispersion of the ore and the optimum conditions required can be readily determined by one skilled in the art.

It has however been found that a pH of from about 9.5 to about 11.0, provided by addition of about 1 to 3 pounds of NaOH per ton of ore, is generally preferred. Other alkaline materials such as KOH or NH OH may be used to provide the desired pH. Dispersants such as sodium silicate, tannins, lignin sulfonates and alkaline phosphates have been found to provide a stable relatively nonsettling suspension. With sodium silicate the optimum quantity is generally from about 1 to about 3 lbs./ ton of ore. Water is usually employed in an amount to provide a slurry containing about 50 to 80 percent solids during grinding.

The discharge from the grinding mill is diluted to 2.5 to 25 percent solids and passed to a cyclone or other classification device, with oversize being returned to the grinding mill. Finished-size feed is then removed by overflow and admixed with flocculating materials (tapioca flour and calcium chloride in figure). Any flocculating materials that cause a selective flocculation of the iron oxide in preference to the silica materials may be used; examples are tapioca flour, potato starch or other flours, natural and modifiedstarches, or polyacrylamides having flocculating properties. Addition of calcium chloride has also been found effective in increasing the settling rates and controlling the amount of suspensoid.

The ore pulp suspension admixed with flocculants is then passed to a thickener where settling and decantation of slimes is effected. In practice the pulp flowing to the thickener will usually contain from about 2.5 to 25 per cent solids comprising up to about 2 pounds of calcium chloride per ton and up to about 2 pounds of flocculants per ton. The action of these chemicals is to produce a rapidly settling flocculated zone comprised chiefly of iron oxide particles while retaining a suspension comprising chiefly slimed silica or silicate particles.

The suspension of silica and silicates is then removed to waste by overflowing. However, other methods such as siphoning or decantation may be used for removal of the suspension. The flocculated solids (underflow) are removed from the thickener and transported to conditioners for conditioning preliminary to flotation. Alternatively, the flocculated solids may be transferred to a second thickener for treatment with additional dispersants and flocculants and the selective flocculation and desliming process repeated in this second thickener. The flocculated underflow from this second desliming process is transferred to the conditioners .while the overflow is transferred to waste.

Following separation of the flocculated underflow from the thickener, suitable conditioning agents are added in the conditioners from which the conditioned pulp is passed to the flotation unit. Addition of conditioning agents directly to the flotation unit rather than to a separate conditioning unit may be advantageous in some cases.

The flotation operation in the method of the present invention is conventional in beneficiation of iron ores. Such processes are described in Bureau of Mines Report of Investigations No. 3799,- March 1945, as well as in US. Patents 2,364,777 and 2,364,778. In the method of the present invention flotation of thesilica (rather than flotation of the iron minerals) is preferred. Either anionic or cationic flotation collectors may be employed, al-

though the anionic reagents generally give best results. However, as stated previously, beneficiation of iron ores by flotation of silica has previously met with very limited success, particularly where fine grinding of the ore is necessary'prior to flotation. Removal of a large percentage of the thus formed silica slimes by the selective flocculation step of the invention enables a much more satisfactory concentrationof iron minerals from ores by the subsequent flotation process.

The following examples will serve to more particularly describe the process of the invention.

EXAMPLE 1 This example illustrates the combination of selective flocculation and anionic flotation of calcium activated silica from afine grained, siliceous iron ore. The ore is Wet ground at 50 percent solids to percent passing 400- mesh with 2.0 lbs. NaOH/ton and 3.0 lbs. sodium silicate/ ton. The NaOH is added to give a pH of about 10 to 11.0 in the ground and diluted pulp. The sodium silicate used is water glass (8.9 percent Na O and 29 percent SiO and serves to give a dispersed pulp.

The ground pulp is then diluted to 17 percent solids and the iron oxide selectively flocculated by addition of 0.25 lb. CaCl -2 H O/ton and 0.5 lb. tapioca flour/ton. The tapioca flour functions as the flocculant while the calcium chloride serves to accelerate formation and settling of the floccules. The flocculated pulp is then deslimed by removal of suspended silica by siphoning. Analysis of resulting slimes is as follows:

Weight percent 22.2 Distribution,'percent Fe 3.8 Grade, percent Fe 6.2

The .deslimed pulp containing selectively flocculated iron oxides is prepared for flotation by dilution to about 30 percent solids. The pulp is then conditioned for about 2 minutes with 1.0 lb. tapioca flour/ton which serves as an iron oxide depressant. NaOH is added in an amount of 2.0 lbs./ton of ore to adjust the pH of the pulp to about 11.5. 0.25 pound of calcium chloride per ton of ore and 1.0 pound tall oil per ton of ore are then added as activator and collector, respectively, for the silica.

The conditioned pulp is then diluted to about 25 percent solids and routed to a flotation cell for aeration and froth removal. By this procedure silica is floated, iron oxides being depressed; the cell underflow is therefore the desired concentrate of iron oxides. This concentrate shows the following analysis:

Weight percent 33.7 Distribution, percent Fe 62.0 Grade, percent Fe 65.6

Percent SiO 3,4

Weight percent 16.7 Distribution, percent Fe 26.9 Grade, percent Fe 57.6

Analysis of the tailing (final froth product) is as follows:

Weight percent 27.4 Distribution, percent Fe 7.3 Grade, percent Fe p 9.5

Amounts and types of reagents employed in the flotation steps may vary considerably, optimum conditions being best determined experimentally in view of the highly empirical nature of the flotation art. Amounts of sodium silicate will usually vary from about 1.0 to about 3.0 or more lbs./ton of ore. Other dispersants such as lignin sulfonate may be used in place of or in addition to the sodium silicate.

Dilutions other than that of the above example may be used in the flocculation step; more dilute pulps usually require more NaOH and sodium silicate. Pulp densities generally range from about 1 to about 25 percent solids.

Flocculating reagents may also vary. Some ores do not require calcium chloride while others may require up to 2.0 lbs./ton or more. Amounts of tapioca flour will usually range from about 0.25 to tbout 2.0 lbs./ton. Other flocculants such as potato starch could also be used.

Concentration of pulp solids during conditioning may vary from about to about 65 percent, though about 30 percent is generally used. Amounts of tapioca flour will depend on usage during selective flocculation and on requirements of the particular ore but generally range from about 0.5 to 2.0 lbs/ton. Other depressants may also be used such as starches, starch derivatives and lignin sulfonates. Conditioning time is usually about one or two minutes.

grained, siliceous iron ore.

chloride furnishes calcium ion that activates silica surfaces for flotation with fatty acids. The conditioning period with calcium salt is usually about 1 or 2 minutes.

In some instances it may be desirable to add calcium as the last reagent in the sequence, following addition of the fatty acid.

The fatty acid used in the above example was a tall oil containing nearly equal amounts of oleic and linoleic acids. Other pure fractions or mixtures of 18-carbon, unsaturated fatty acids of animal or vegetable origin could be used with varying degrees of effectiveness. Fatty acids of other chain lengths may also be satisfactory for some ores. Amounts of fatty acid up to about 3 lbs./ ton of ore are generally satisfactory. Fatty acid soaps, such as sodium soaps, may also be used as collector.

in place of the fatty acids. Conditioning time with the fatty acid will vary upwards to as much as 15 minutes with about 3 minutes usually being adequate.

In the method of the example a frother is generally not necessary, although about 0.1 lb. of pine oil/ ton may be used in some instances.

EXAMPLE 2 This example illustrates the combination of selective flocculation and cationic flotation of silica from a fine tionsof cationic collectors are employed for greater effectiveness; a single addition of collector may also be employed.

The ore is wet ground at 50 percent solids to per-- cent passing 400-mesh, with 1.0 lb. NaOH/ton and 1 lb. sodium silicate/ton and then diluted to 17 percent solids.

The iron oxides are selectively flocculated by 0.75 lb. tapioca flour per ton of ore Without the use of calcium chloride;

is as follows:

Weight percent 20.0 Distribution, percent of Fe 5.5 Grade, percent of Fe 10.0

The deslimed pulp is diluted to about 30 percent'solids and is then conditioned for 1 minute with 0.1 lb. of Ar-- quad C/ton, 0.12 lb. kerosene containing 10 percent silicone/ton and 0.06 lb. pine oil/ton. The Arquad C, an

alkyl quaternary ammonium chloridea mixture of 8 l to 18 carbon chain amines, is a weak silica collector; 1

cyclic tertiary amines (imidazolines) have also been used at this stage.

In this example prior conditioning with tapioca flour to depress iron is not employed, residual tapioca from the selective flocculation step serving this purpose. Prior conditioning with tapioca flour may however be desirable with certain ores.

Pulp pH is that obtained upon dilution-about 9.5.. The kerosene-silicone mixture serves to modify the froth structure and the pine oil is added for frothing properties.

A first rougher flotation is accomplished by diluting the I pulp to 25 percent solids, aerating and froth removal.

Depressed iron is contained in the cell underflow while the froth contains silica. tion the pulp is conditioned 2 minutes with 0.75 lb. of tapioca flour/ton (for suppression of iron oxides) and for an additional 1 minute with 0.15 lb. Armac 12D/ton.

Armac 12D, a 12-carbon aliphatic amine-acetate, is a In the example, stage addi- Suspended silica (slimes) is removed from the. flocculated pulp by overflowing. Analysis of the slimes Following this rougher flota stronger collector than Arquad C but more expensive than the latter. Its purpose is to collect the more difiicultly floatable course quartz and silicates. Other primary and secondary aliphatic amines, as pure fractions ing Examples 3 and 5, note that slime products of EX- ample 5 contain 6.1 percent Fe in highest grade product, whereas slime of Example 3 ranged from 36.9 to 40.6 percent Fe. Flotation tests described in Examples 4 and or mixtures having 8 to 22 carbon atom chains may be 5 5 employed anionic methods for flotation of silica. Exused with varying degrees of etfectiveness. Amines are ample 11, also on ore A, describes a flotation test made customarily neutralized before flotation by reacting with after selective flocculation and deslimin g, but differs from hydrochloric or acetic acid, thereby increasing water Example 5, in that cationic reagent (Armac C) was used solubility. Generally amounts greater than about 0.5 as silica collector instead of fatty acid. lb./ton are not used because of reagent costs. Examples 6, 7, 8, 9 and 10 describe tests on iron ore A second stage rougher flotation is then accomplished B. Example 6 shows results of simple dispersion and by aerating and froth removal, the cell underflow again deslimin-g practiced on material ground so that 88 perconstituting the flotation concentrate. Analysis of the cent passes 400-mesh sieve. Only slime #1 is of sigconcentrate is as follows: nificant weight, and contained 28.2 percent Fe. Example Weight ercent 35 2 7 lists anionic flotation results obtained on ore B, without desliming of any type. Example 8, illustrates the prac- Distnbutlon, percent Fe 64.2

t1ce of flotanon after selectlve flocculation and desliming. Grade, percent Fe 66.8 Percent Sio 4 0 While concentrate grade shown under Example 8 is not 2 "T" improved significantly, improvements were obtained in A cleaner flotation step is then carried out 1n whlch recovery (distribution) of iron in concentrate. The slime froths from first and second rougher stages arecombined product in Example 8 is of reduced weight and iron for cleaning by recycling through the flotation step withcontent from slime product #1, Example 6; reduction out additional reagents. The froths are subjected to two in iron content and weight is attributed to practice of cleaning operations to give a composite middling having selective flocculation. Examples 9 and 10 show the practhe following analysis: '25 tice of selective flocculation and flotation where potato Weight percent starch was substituted in part for tapioca flour as the Distribution percent Fe 216 fl cculant, and (Example 10) where Marasperse (lignm sulfonate) was substituted for sodium silicate. Grade, percent Fe 45.3

Example of practice of the invention on a third ore Analysls of the final broth, 1.e.,'ta1l1ngs is as follows: i given in Examples 1 12 and 13 Example 12 in Weight percent 25 7 trates the practice of desliming alone, in the presence of Distribution, percent Fe 7 dispersants, and shows a high weight of slime product Grade, percent Fe 9 Containing 22.5 percent Fe and contributing to loss of As in the case of processes employing anionic col- 6- Percent Offhe unit} mp 13 illustfafes lectors (Example 1), specific types and amounts of laboratory flotation w thout either deslnnm-g or selective agents using cationic collectors may vary widely and are and deshmlng; not: that concentrate best determined empirically contains 64.2 percent Fe, 4.6 percent S10 and recovers 52.1 percent of iron in the sample. Data given in EXAMPLES 343 Example 1, above, shows, when compared to Example Table 1 gives reactants and results of laboratory hench- 40 12, a reduced iron content and loss in slime product due scale experiments that further illustrate the variety of to practice of select1ve flocculation. Comp possible applications of the process of the invention and tween concentrates, EXampleS 1 Show all the advantages derived therefrom. A description of ores P Q f and almost 10 P cent greater Fe fecovfify A, B and c employed i these examples i given i m (distributlon) as a result of prior selective flocculation. 2 below Tests were also run in the pilot plant on a continuous E l 3, 4 d 5 pertaining to ore A ground to basis, u s1ng ore C, which confirmed laboratory results, 100 percent passing 325- h, h th following: E in proving that beneficial effects are obtained from seanrp1o 3 d ii i f il i di i f li i h lective flocculation and deslimirig ahead of flotation. sodium hydroxide and sodium silicate, resulted in slime Becajflse the 1311011 P W n t mad with the products totaling 62.7 percent of total weight, with slime sgficlfic p p f pr ving the pr C F, Results are Hot d t f equal} or hi h i l i h h Corndirectly comparable to those obtamed 1n the laboratory. posite head (original ore). Example 4'lists metallurgical However, data obtamed showed that selective floccularesults obtained on ore sample A, by flotation without U011 3 de$11I I11I1g W111 WOI'k f dynamic Conditions desliming. Example 5 .gives the metallurgical results PP PllOt P 4 and 15 not C d o Static obtained by flotation after dispersion, selective flocculal'ldltlOllS that preva1l n batch laboratory testing. tion, and triple decantatinn f slimes Note i d Results of these continuous circuit flotation operations concentrate grade, d hi h di t ib i value of F are shown in Table 3 (without selective flocculation) in concentrate as compared to Example 4. In comp-arand in Table 4 (with selective flocculation).

TABLE 1 Analysis, percent Reagents, Amount, lbJT.

Distrl- Wt.-perbution Ex. Ore Product cent percent Type Selective Grind Fe S102 Fe Desliming Floccula- Flotation tion and Desliming 3 A Deslimed Sand 37.3 50.4 27.6 51.2 -NaOH 2.0 325mesl1.

Slimes #1 36.9 21. 3 69.3 21. 4 Sodium Silicate.-- 1. 0 Slimes 15.9 37.8 45.0 16.4 Slimes #3 9.19 40. 6 41. 5 11.0 Composite Head 100.0 36.7 47.1 100.0

4 A Concentrate. 401 62.8 69.6 4.0 325 mesh.

Middling 1 13.8 47.6 13.3 1. 0 Middling2 7.8 27.3 5.9 Tapioca Flour 1. 5 Middling 3 6. 4 14. 2 2. 5 Fatty acid 0 Tailing 31. 9 4. 3 3. 7 Composite Head 100.0 36.1 100.0

TABLE 1.Continued Analysis, percent Reagents, Amount, lb./T.

Distribution Product percent Type Selective Gn'nd Fe S103 Fe Desliming Floccula- Flotation tion and Desliming 41. 3 64. 6 73. 6 325 mesh. 10. 3 51. 9 14.8 Sodium Silica 4. 4 29.2 3. 5 03.01:. 2HzO 17. 5 8. 9 4.3 Tapioca Flour 16. 9 6. 1 2. 8 Fatty acid.

5. 2 3. 0. 4 4. 4 4. 2 0. 6 Composite Head 100. 0 36. 3 100.0

Deslimed Sand 65. 6 31. 9 68.5 NaOH 88% minus imcs 33. 28. 2 30. 9 Sodium Si1icate 400-mesh. Slimes #2 O. 9 20. 6 0. 6 Composite Head- 100. 0 30. 6 100. 0

27. 6 59. 8 52. 5 4. 0 88% rniuls 14. 0 52. 6 23. 4 2. 0 400-mcsh.

8. 8 39. 5 11. 0 2. 0 49. 6 8. 3 13. l 2. 0 Composite Head" 100. 0 31. 5 100. 0

Concentrate 32. 9 60. 3 5. 9 63. 1 NaOH 2.0 3. 0 88% minus 10. 5 47. 6 15. 9 Sodium Silicate. 1. 0 400-mesh.

6. 0 5.0 CaClz. 2H2O 1. 5 1. 0 35. 0 5. 0 Tapioca FlOllL. 0. 5 1. 5 15. 6 11. 0 Fatty acid 1. 0 100. 0 100. 0

31. 8 62. 4 2. 0 3.0 88% minus 9. 7 15. 6 1. 0 400-mcsh. 5. 3 4. 6 1. 0 31. 5 5. 3 0. 5 1. 0 16. 5 11.1 Tapioca Flour- 0. 5 1. 5. 2 1. 0 Fatty acid. 1. 0 Composite Head 100. 0 100. 0

Concentrate 30. 7 60. 1 NaOH 2. 0 3. 0 88% 400- Middling 1 11. 1 17. 5 Marasperse C. 0. 25 mesh. Middling 2 6. 1 5. 3 1. 0 Tai1ing 32. 0 4. 8 Slimes 20. l 12. 3 Composite Head 100. 0 100. 0

Concentrate 35.8 64. 8 325 mesh. Middling 1 10. 8 16. 7 Middling 2- 5. 6 6. 0 Tailin 15. 2 6. 2 Tapioca Flour 0. Slimes #1. 29. 0 5. 8 Armac C 0. 25 Slimes #2 3. 6 0. 5 Frother 0. 08 Composite Head. 100. 0 100. O

Deslimed Sand. 57. 6 73. 6 NaOH 2. 0 96% minus Slimes 42. 4 26. 4 Sodium Silicate--. 3.0 400-mesh. Composite Head. 100. 0 100. O

29. 2 52. 1 NaOH 4. 0 14. 3 23. 5 Tapioca Flour- 1. 5

7. 8 10. 3 CaClz.2HzO 0. 5 96% minus 48. 7 14. 1 Fatty acid 1. 0 4004110511. Composite 100. 0 100. 0

TABLE 2 Chemical Analysis, percent Ore Designation Mineralogical Description Fe SiO A 36. 0 47. 3 Contains chiefly hematite and quartz, with a relative abu a ce o m g e Goethite is almost completely absent. Average hematite-magnetite aggregates to microns in size, but contain silica inclusions. Hemat te-magnetite contains lattice-like silica intergrowths 2 to 4 microns wide. Silica contains disseminated iron oxide.

B 30. 2 51. 8 Goethite chief iron mineral, but also contains smaller amounts 0 e a e 4 magnetite. Quartz and chert present as gangue. Goethlte occurs as massive grains with quartz intergrowths, and mixtures with hematite-magnetite and silica-including finely disseminated assemblages. In addition to quartz, about 34 volume is chart with finely dissemlnated hematite of less than 10 microns to less than 1 micron in size.

0 36. 1 47. 1 Contains chiefly hematite and quartz, with residual magnetite andflllifwr amounts of goethite. Most of hematite ranges from 40 to microns 111 size, with simple types of locking. Minus 40-micron hematite shows more complex types of locking.

TABLE 3 [Continuous Circuit Flotation Results: Ore C 1 without Selective Flocculation] Reagents Analysis, percent Product Weight, Distribution, Total amount, lb./long percent percent Fe ton of- Type Fe SiOg Feed Concentrate Concentrate 42. 9 75. 4. 07 9. 50 Tailing 53. 5 21. 5 1. 17 2. 72 Thickener 1 Overflow, 3. 6 3. 5 1. 3. 39 Composite, Tailing and 57. 1 25.0 Tall oil fatty acid 2. 62 6. 11

Thickener l Overflow.

Composite, Head Sample 100. 0 100.0

1 Nominal grind, 95 percent minus loo-mesh.

Sub-sieve Analysis of products:

Avg. particle dia., Specific surface,

microns cmfi/ gm Cyclone overflow 4. 7 3, 800

Thickener overflow 1. 7 11, 900

Thickener underflow 5. 6 3, 200

Concentrate 2. 5 4, 900

Tailing 5. 9 3, 200

TABLE 4 [Continuous Circuit Flotation Results; Ore C With Selective Flocculation at 10 Percent Solids Reagents Analysis, percent Product Weight, Distribution, Total amount, lb.llong percent percent Fe ton of- Type Fe SiOg Feed Concentrate Concentrate 46. 5 65.1 4. 8 83. 7 NaOH 4. 1.5 8. 92

Tailing 43. 0 9. 9 11. 8 Sodium Silicate 2. 07 4. 46

Thickener 1 Overflow 10. 5 15. 4 4. 5 Calcium chloride 0.88 1. 90

Composite, Tailing and 53. 5 11.0 16. 3 Tapioca flour 1, 29 2. 78

Thickener 1 Overflow.

Composite, Head Sample 100. 0 36. 2 100. 0 Tall oil fatty acid 1. 24 2. 67

1 Grind, 93 percent minus loll-mesh.

What is claimed is:

1. A process for concentration of iron ores comprising the following sequence of steps (1) initially forming a relatively stable aqueous dispersion of the ore, (2) treating the dispersion of ore with a flocculating agent capable of causing selective flocculation of the iron oxides in the ore in preference to silica materials, and selected from the group consisting of starches, flours, and polyacrylamides (3) allowing the flocculated iron oxides to settle, (4) separating and removing the suspended silica materials from the flocculated iron oxides and (5) subsequently subjecting an aqueous pulp of the flocculated iron oxides to a froth flotation operation in the presence of a c-ollecor to further separate iron oxides from siliceous materials.

2. The method of claim 1 in which the initial aqueous dispersion of the ore is achieved by use of a dispersing agent comprising a combination of NaOH and sodium silicate.

3. The method of claim 1 in which the flocculating agent employed to effect the selective flocculation is tapioca flour.

4. The method of claim 3 in which calcium chloride is additionally added to improve selective flocculation.

5. The method of claim 1 in which the suspended silica materials are separated from the flocculated iron oxides by decantation.

6. The method of claim 1 in which the suspendedsilica materials are separated from the flocculated iron oxides by overflowing.

References Cited by the Examiner UNITED STATES PATENTS 2,149,748 3/1939 Samuel 209'5 X 2,217,684 .10/1940 Kirby 209166 2,322,201 6/ 1943 Jayne 209-166 2,381,514 8/ 1945 Phelps 209-5 2,383,467 '8/19'45 Clemmer 209-166 2,660,303 1 1/ 3 Haseman 2095 2,740,522 4/ 1956 Aimone 209166 OTHER REFERENCES Melcher et al., Mining Congress Journal, vol. 49, p. 29, December 1963.

HARRY B. THORNTON, Primary Examiner.

ROBERT HALPER, Assistant Examiner. 

1. A PROCESS FOR CONCENTRATION OF IRON ORES COMPRISING THE FOLLOWING SEQUENCE OF STEPS (1) INITIALLY FORMING A RELATIVELY STABLE AQUEOUS DISPERSION OF THE ORE, (2) TREATING THE DISPERSION OF ORE WITH A FLOCCULATING AGENT CAPABLE OF CAUSING SELECTIVE FLOCCULATION OF THE IRON OXIDES IN THE ORE IN PREFERENCE OF SILICIA MATERIAL, AND SELECTED FROM THE GROUP CONSISTING OF STARCHES, FLOURS, AND POLYACRYLAMIDES (3) ALLOWING FLOCCULATED IRON OXIDES TO SETTLE, (4) SEPARATING THE REMOVING THE SUSPENDED SILICA MATERIAL FROM THE FLOCCULATED IRON OXIDES AND (5) SUBSEQUENTIALLY SUBJECTING AN AQUEOUS PULP OF THE FLOCCULATED IRON OXIDES TO A FROTH FLOTATION OPERATION IN THE PRESENCE OF A COLLECTOR TO FURTHER SEPARATE IRON OXIDES FROM SILICEOUS MATERIALS. 